There is made a study in which a biphenyl compound and formaldehyde are subjected to a condensation reaction to thereby obtain an aromatic hydrocarbon resin (see Non Patent Document 1).
It is further known that in the usual reaction condition in which an aromatic hydrocarbon formaldehyde resin is produced by a reaction of an aromatic hydrocarbon with formaldehyde, diarylmethanes formed from two molecules of aromatic hydrocarbons and one molecule of formaldehyde are produced, and remain as unreacted components also after modification, so that the mechanical strength and the thermal decomposition resistance of cured products obtained from the modified resin decrease. Then, there is made an attempt of suppressing the formation of the diarylmethanes by controlling the reaction condition (see Patent Document 1).